1. Field of the Invention
This invention relates to improved catalytic reaction systems and to methods for catalytic reaction of carbon containing compounds. In one specific aspect the present invention relates to quick lightoff, fast thermal response catalysts for use in exhaust gas catalytic converters.
2. Brief Description of the Prior Art
Automotive emissions are still a major environmental problem in spite of the major advances brought about by the use of catalytic converters. One factor limiting the performance of catalytic converters is that pollution is not controlled during the thirty or more seconds required to bring the converter catalyst to its operating temperature. In present converters, warm-up is dependent on heating of the catalyst by hot engine exhaust gases. Although electrical heating could be utilized to preheat the catalyst prior to engine operation, the power and the time delay required with present catalyst structures, ceramic or metal, have been deemed unacceptable.
Subsequent to catalyst light-off, surface reactions on conventional monolithic catalysts such as are used in catalytic converters are mass transfer limited. Thus, the catalyst mass required for a given conversion level is much higher than if no mass transfer limitation existed at the given operating conditions. The high catalyst mass required for the required conversion level results in the relatively long heat-up times experienced, even with electrical heating.
The need to reduce catalyst warm-up time of the conventional ceramic monolith automotive catalysts to reduce emissions during the warm-up period has led to increased interest in metal monolith catalysts. However, merely substituting metal for ceramic in a conventional monolith structure yields catalysts which still have much too high a thermal mass. The short channel length catalysts of my prior U.S. Pat. No. 5,051,241 offer the low thermal mass and high conversion efficiencies required. For automotive applications, packaging of such catalysts into a rugged assembly tolerant of flow pulsations is required to meet the new 100,000 mile durability requirements.
The present invention makes possible rugged fast light-off catalytic converters for automotive engine exhaust control which utilize short channel length catalysts such as those of the above cited patent.